Indoor Distance Research Articles

A Combined Filtering Method for ZigBee Indoor Distance Measurement.

Indoor distance measurement technology utilizing Zigbee's Received Signal Strength Indication (RSSI) offers cost-effective and energy-efficient advantages, making it widely adopted for indoor distance measurement applications. However, challenges such as multipath effects, signal attenuation, and signal blockage often degrade the accuracy of distance measurements. Addressing these issues, this study proposes a combined filtering approach integrating Kalman filtering, Dixon's Q-test, Gaussian filtering, and mean filtering. Initially, the method evaluates Zigbee's transmission power, channel, and other parameters, analyzing their impact on RSSI values. Subsequently, it fits a signal propagation loss model based on actual measured data to understand the filtering algorithm's effect on distance measurement error. Experimental results demonstrate that the proposed method effectively improves the conversion relationship between RSSI and distance. The average distance measurement error, approximately 0.46 m, substantially outperforms errors derived from raw RSSI data. Consequently, this method offers enhanced distance measurement accuracy, making it particularly suitable for indoor positioning applications.

Compact BLE Antenna With a Modified PIFA Configuration for Wearable EMG Monitor

An antenna mounted underneath the top cover of a wearable device, fed by an ultra-low-profile connector, is proposed for Bluetooth-Low-Energy (BLE) communication at 2.4 GHz. As the antenna is to be used for a wearable device, it is essential that it should be compact in size and tolerant against the nearby medium change. The modified planar inverted-F antenna (PIFA) that we propose consists of a main patch and a parasitic element to broaden the antenna bandwidth. The end of the parasitic element is shorted to miniaturize the antenna to 25 by 10.8 millimeters, fitting well inside a watch-type wearable device. Also, the complete ground layer of the antenna makes it radiate well in the outward direction, and minimally interact with the back-side medium. This results in the reflection coefficient being insensitive to the medium change on the backside. The proposed antenna has a peak gain of 3.62 dBi along with 20% efficiency and the impedance bandwidth of 80 MHz (2.4 ~2.48 GHz). To examine the communicative operation of the antenna in practice, the received signal strength indicator (RSSI) of the complete prototype device with the antenna is measured in various postures and orientations, demonstrating reliable connectivity within a typical indoor distance of 10 meters. Lastly, the antenna is embedded in a wearable device, demonstrating electromyography’s wireless monitoring.

Improving the Accuracy of Estimates of Indoor Distance Moved Using Deep Learning-Based Movement Status Recognition.

As a result of the development of wireless indoor positioning techniques such as WiFi, Bluetooth, and Ultra-wideband (UWB), the positioning traces of moving people or objects in indoor environments can be tracked and recorded, and the distances moved can be estimated from these data traces. These estimates are very useful in many applications such as workload statistics and optimized job allocation in the field of logistics. However, due to the uncertainties of the wireless signal and corresponding positioning errors, accurately estimating movement distance still faces challenges. To address this issue, this paper proposes a movement status recognition-based distance estimating method to improve the accuracy. We divide the positioning traces into segments and use an encoder–decoder deep learning-based model to determine the motion status of each segment. Then, the distances of these segments are calculated by different distance estimating methods based on their movement statuses. The experiments on the real positioning traces demonstrate the proposed method can precisely identify the movement status and significantly improve the distance estimating accuracy.

Practical approximate indoor nearest neighbour locating with crowdsourced RSSIs

In the indoor space, finding the nearest neighbour is of great importance in location-based services. Received Signal Strength Indication (RSSI) has received much attention due to its simplicity and compatibility with existing hardware, which has been widely used for indoor localization. Existing indoor nearest neighbour search methods are based on the real walking distance, which need ground survey and much labor work to measure many real distances. Crowdsourcing is a low-cost and efficient way to collect the RSSI of indoor space without expert surveyors and designated coordinates for RSSI collection points. The crowdsourced RSSIs can reflect the location of indoor objects and RSSI-based localization method is the simplistic method as it needs low hardware requirements, low deployment cost and no survey indoor distance. So we study how to search the nearest neighbour of indoor objects with crowdsourced RSSIs. To address this problem, we propose a graph with interval weights, called I-graph, which can connect the RSSIs and represent the topology of indoor space. We also construct a search tree index D-tree, which can index the graph with interval weights and search the nearest neighbour objects efficiently. We also propose a novel distance metric for RSSI and study the relationship between the RSSI distance and the indoor distance. To locate nearest neighbour of indoor objects with crowdsourced RSSIs, we devise efficient search algorithms and pruning strategies for computing the nearest neighbour query. We demonstrate the efficiency and effectiveness of the proposed solution through extensive experiments with two real data sets.

Towards Indoor Temporal-variation aware Shortest Path Query

The recent years have witnessed the growing popularity of indoor location-based services (LBS) in practice and research. Among others, indoor shortest path query (ISPQ) is of fundamental importance for indoor LBS. However, existing works on ISPQ ignore indoor temporal variations, e.g., the open and close times associated with entities like doors and rooms. In this paper, we define a new type of query called Indoor Temporal-variation aware Shortest Path Query (ITSPQ). It returns the valid shortest path based on the up-to-date indoor topology at the query time. A set of techniques is designed to answer ITSPQ efficiently. We design a graph structure (IT-Graph) that captures indoor temporal variations. To process ITSPQ using IT-Graph, we design two algorithms that check a doors accessibility synchronously and asynchronously. Furthermore, we propose a novel index structure (IT-Index) that extends the state-of-the-art index significantly by storing dynamic door-to-door distances in a compact distance cube associated with tree nodes. When processing ITSPQ using IT-Index, we make use of the distance cube to avoid time-consuming indoor distance computation on-the-fly. We evaluate the proposed techniques using extensive experiments on synthetic and real data. The results show that our IT-Index based method is the most efficient for processing ITSPQ at a modest cost of index memory consumption.

SCIENTIFIC SUBSTANTIATION OF OPTIMIZATION OF HYDROAEROINE AIR COMPOSITION IN PUBLIC PREMISES FOR PERSONS WITH SPECIAL NEEDS

The purpose of this work is scientific substantiation and optimization of hydroaeroionic composition of air in public places to create safe living and working conditions for people with special needs using a modern ultrasonic ionizer. Measurements were performed by the developed method using an air saion counter "Sapphire 3K" and using a thermoanemometer TM-4001. To perform the analysis of experimental research data, the method of mathematical planning of the experiment according to the scheme of rotatable central composite planning (RCCP) was used, which is based on regression analysis. The possibility of using for the process of hydroaeroionization of premises where there are people with special needs of saline solutions of different degrees of concentration to increase the concentration of negative ions has been investigated. Analysis of experimental data showed that increasing the concentration of saline solutions leads to a decrease in the intensity of formation of hydroaeroions in the room. Minimizing the mineralization of water will allow you to get the optimal concentration of hydroaeroions with artificial ionization of the room where people with disabilities are. Mathematical processing of the obtained data allowed to establish the combined effect of indoor air velocity (v) and distance to UGA (s) on the concentration of positive and negative aerons when using mineralized water of different degrees of concentration. The obtained result can be applied at designing and development of control system of the ultrasonic generator of air ions for the purpose of creation of the most comfortable high-quality ionized air in rooms where there are persons with special needs.: Synthesized regression models of concentrations of hydroaeroions, which describe the relationship between the velocity of air in the room and the distance to the ultrasonic generator of air ions during artificial ionization of rooms for people with special needs. The adequacy of the models is checked by the coefficient of determination, which proves the high level of correlation of the system coefficients.

Understanding Sub-GHz Signal Behavior in Deep-Indoor Scenarios

Critical Internet-of-Things (IoT) services require seamless connectivity, which is not always simple to provide and particularly in deep-indoor scenarios, it can be even impossible in some cases. The existing outdoor-to-indoor path-loss models lack accuracy in underground situations, thus IoT coverage planning in such areas cannot rely on robust tools and becomes a process of trial and error. In this work, we derive and analyze various environmental features that can be useful in understanding sub-GHz deep-indoor signal propagation. Based on a large-scale field trial in an underground tunnel system, we formulate several parameters related to the TX-RX distance and tunnel geometry. Through feature relevance studies in linear (ordinary least-squares (OLS) regression) and nonlinear (the Gaussian process regression) realms, we show that 2-D indoor distance and the distances to the tunnel walls may be useful in sub-GHz signal strength prediction in deep-indoor situations. We construct a linear and a Gaussian process model for the indoor path-loss prediction that outperforms the 3rd Generation Partnership Project (3GPP) model by 1.8 and 4.1 dB, respectively.

Time of arrival measurement for indoor distance monitoring in 130-nm CMOS

A new architecture for Vernier-based frequency-to-voltage/digital converter (VFVDC) is proposed for time difference of arrival (TDOA) measurement using a frequency domain approach. The VFVDC is employed for indoor distance monitoring using an RFID front end. The proposed architecture employs an injection-locked ring oscillator (ILR) as the clock source. The proposed ILR oscillator does not need the complex calibration procedures, usually required by Phase Locked Loop (PLL) based oscillators in Vernier-based time-to-digital converters. The oscillator consumes 14.4 μW and 1.15 mW from 0.4 V and 1.2 V supplies. The total power consumption of the entire chip is only 0.65 mW and 7.6 mW from 0.4 V and 1.2 V supplies while operating at 1.615 MHz and 22.55 MHz, respectively. The design was implemented in 130-nm CMOS process and has a core area of 0.1 mm2, one of the lowest in reported literature. The proposed VFVDC is reconfigurable and achieves a large detectable range of 1–300 mm, with a fine distance resolution of 3 mm/kHz in a small die size while consuming low power with FoM of 5.78 fA-s/m.

The correlations between distance stereoacuity and levels of control at different far distances in children with intermittent exotropia

Objective: To study the correlations between the distance stereoacuity and the levels of control at different far distance fixations in children with intermittent exotropia. Methods: In this prospective, non-interventional case series study, 52 children with intermittent exotropia (basic, divergence excess and pseudo-divergence excess types, exodeviation angles≥15 PD) admitted to the Shandong Provincial Hospital Affiliated to Shandong University for surgery between August 2014 and March 2015 were enrolled. The distance stereoacuity was tested with the distance Randot stereotest, and the control of exodeviation was assessed at outdoor far distance fixation of 50 m, indoor far distance fixation of 30 m, and indoor distance fixation of 3 m, respectively, using the office-based 6-point control scale proposed by Mohney and Holmes. The distance stereoacuity and control scores of every intermittent exotropia child were tested 3-4 times in a single day with an interval of at least 2 hours. Nonparametric Spearman rank method was used to analyze the correlations between distance stereoacuity and levels of control at three different far distances in children with intermittent exotropia. Results: The mean age of 52 enrolled children (26 males, 26 females) was 7 years (range, 5-12 years), and 192 groups of distance stereoacuity and control scores were got for the 52 children. Positive correlations between the distance stereoacuity and the levels of control at outdoor far distance fixation of 50 m, indoor far distance fixation of 30 m, and indoor distance fixation of 3 m were observed (coefficients of correlations; r=0.489, 0.472, 0.282, all P<0.001). Conclusion: There are correlations between the distance stereoacuity and the levels of control at outdoor far distance fixation of 50 m, indoor far distance fixation of 30 m and indoor distance fixation of 3 m in children with intermittent exotropia, and the former two are found to be stronger than the latter one. (Chin J Ophthalmol, 2019, 55:25-30).

π-Splicer: Perceiving Accurate CSI Phases with Commodity WiFi Devices

WiFi technology has gained a wide prevalence for not only wireless communication but also pervasive sensing. A wide variety of emerging applications leverage accurate measurements of the Channel State Information (CSI) information obtained from commodity WiFi devices. Due to hardware imperfection of commodity WiFi devices, the frequency response of internal signal processing circuit is mixed with the real channel frequency response in passband, which makes deriving accurate channel frequency response from CSI measurements a challenging task. In this paper, we identify non-negligible non-linear CSI phase errors and report that IQ imbalance is the root source of non-linear CSI phase errors. We conduct intensive analysis on the characteristics of such non-linear errors and find that such errors are prevalent among various WiFi devices. Furthermore, they are rather stable along time and the received signal strength indication (RSSI) but sensitive to frequency bands used between a transmission pair. Based on these key observations, we propose new methods to compensate both non-linear and linear CSI phase errors. We demonstrate the efficacy of the proposed methods by applying them in CSI splicing and indoor distance ranging. Results of extensive real-world experiments indicate that accurate CSI phase measurements can significantly improve the performance of splicing and the stability of the derived power delay profiles (PDPs). Moreover, the estimated distance errors are reduced by 5.7 times on average comparing to the state-of-the-art schemes.

Indoor distance estimation for passive UHF RFID tag based on RSSI and RCS

We develop a new procedure to estimate the indoor distance for passive UHF RFID tag, the estimation concept relies on the relationship between radar cross section RCS of the maximum effective reading distance and any measured distance at 928 MHz multiplied by received signal strength indicator RSSI ratio. It gives a high accuracy in two stages. In the first stage, the percentage accuracy of the estimated distance is trained, and a percentage polynomial curve is created; this curve is used to increase the accuracy in the second stage which ranges from 90.3% to 100.0% with root mean square error RMSE 0.02.

Far distance control scores for assessing intermittent exotropia

To assess the level of control in intermittent exotropia by applying the office-based 6-point control scale to far-distance testing. Fifty-two children with intermittent exotropia were enrolled in this prospective, noninterventional case series. Control of exodeviation was assessed at indoor distance (ID) of 3m and near distance of 33cm using the office-based 6-point control scale, which was additionally applied to indoor far distance (IFD) fixation of 30m and outdoor far distance (OFD) fixation of 50m. In all 52 patients, the level of control at OFD fixation was either worse than (31%) or the same as (70%) the level of control at IFD fixation and the level of control at IFD fixation was worse than (64%) or the same as (35%) the level of control at ID fixation. The level of control at OFD fixation was worse than (69%) or the same as (31%) the level of control at ID fixation for all 52 patients. The differences between mean control scores of OFD and IFD fixation (P=0.002), IFD and ID fixation (P<0.001), OFD and ID fixation (P<0.001) were statistically significant. The outdoor and indoor far distance control scores can increase the sensitivity of the office-based 6-point control scale. The office control scale for assessing control in patients with intermittent exotropia could have application for the management of intermittent exotropia.

Indoor and Outdoor Distance Estimation for Accelerometer-Derived Proximity Data

Indoor and Outdoor Distance Estimation for Accelerometer-Derived Proximity Data

A Standard Indoor Spatial Data Model—OGC IndoorGML and Implementation Approaches

With the recent progress in indoor spatial data modeling, indoor mapping and indoor positioning technologies, several spatial information services for indoor spaces have been provided like for outdoor spaces. In order to support interoperability between indoor spatial information services, IndoorGML was published by OGC (Open Geospatial Consortium) as a standard data model and XML-based exchange format. While the previous standards, such as IFC (Industrial Foundation Classes) and CityGML covering also indoor space, aim at feature modeling, the goal of IndoorGML is to establish a standard basis for the indoor space model. As IndoorGML defines a minimum data model for indoor space, more efforts are required to discover its potential aspects, which are not explicitly explained in the standard document. In this paper, we investigate the implications and potential aspects of IndoorGML and its basic concept of the cellular space model and discuss the implementation issues of IndoorGML for several purposes. In particular, we discuss the issues on cell determination, subspacing and the hierarchical structure of indoor space from the IndoorGML viewpoint. Additionally, we also focus on two important issues: computation of indoor distance and the implementation of indoor context-awareness services based on IndoorGML. We expect that this paper will serve as a technical document for better understanding of IndoorGML throughout these discussions.

Modulation and Coding Scheme (MCS) for Indoor Image Sensor Communication System

In this paper, we propose an indoor image sensor communication (ISC) system comprising an attentive indoor environment in which rolling-shutter cameras (including smart phone cameras) are used to receive data from light sources. The challenges of intended system mainly come from the receiver side, including its rolling shutter mechanism, its low and time-variant frame rate (e.g., no greater than 30 fps), and the narrow bandwidth response (i.e. several kHz baseband). Also, the requirements of flicker-free modulation enabling the dimming capacity, and indoor distance (i.e., up to 10 m) are unmitigated challenges. To resolve all mentioned challenges, we propose new hybrid modulation schemes, including M-ary frequency-shift keying (M-FSK) modulation and a hybrid modulation of M-FSK and phase-shift keying (2-PSK) for ISC. Simulation, numerical analysis and experiment results are given to illustrate the feasibility of the intended system.

Thermal Performance Comparison between Single and Double Storey Terrace Houses in Melaka, Malaysia

Over the past decade many studies were conducted to investigate the thermal performance of terraced houses in Malaysia. It was found that this housing typology failed to address the need for thermal comfort and alternatives to the narrow frontage with deep plan have been proposed with simulated good thermal performance. Although this is good progress for new generation of terraced houses, millions of units of terraced houses are still in use and new units with the outdated existing plans continued to get built due to consistently very high demand due to progressive urbanisation and rapid economic developments. Therefore, it is imperative that the thermal comfort issue for existing terraced houses is dealt with and through this paper a comparison between single and double storey terraced houses is made through analysis of indoor environmental monitoring (ambient temperature, relative humidity and air velocity) of two (2) selected case studies in Merlimau, Melaka. Contrary to popular belief, it is found that there is no statistical difference between both sets of indoor temperature and relative humidity between the case studies. This finding is indicative of the consistent and stable temporal temperature highs and lows in a 24 hour cycle despite the difference in indoor volume and distance between the ground floor and the roof cavity. Much of the reason is due to the materiality of the terraced houses construction and unsealed and uninsulated building envelope. Therefore, further research into improving the thermal performance of existing terraced houses of any typology have to be conducted to allow thermal comfort and to reduce reliance on high energy consuming air-conditioning.

Symmetrical Full-Duplex Integrated Passive Optical Network and Optical Wireless Communication Transmission System

We propose and experimentally demonstrate a full-duplex integrated passive optical network (PON) and indoor optical wireless communication (OWC) system. For the PON part, an external cavity laser (ECL) and a directly modulated laser (DML) are used as optical sources for downlink and uplink, respectively. The OWC subsystem utilizes a visible light-emitting diode (LED) for downlink and an infrared LED (IR-LED) for uplink transmission. To enable high spectral efficiency (SE), high-speed transmission, and flexible multiple access with simplified optical network unit (ONU)-side digital signal processing (DSP), multilevel, multiband quadrature amplitude modulation (QAM) and hybrid 128/64/16 Nyquist single-carrier frequency domain equalization (N-SC-FDE) modulation are implemented in this paper. In terms of 62.5 MHz OWC N-SC-FDE signals, the system successfully delivered a further 140 cm indoor distance after transmitting over a span of 25 km standard single mode fiber (SSMF) together with three subbands of 250 MHz PON signals. As a proof of concept, an integrated system of symmetrical full-duplex 5 Gb/s PON and 250 Mb/s OWC at each direction for three wired users and one wireless user is successfully achieved. The measured bit error ratios (BERs) for each user are all smaller than the 7% pre-forward-error-correction (pre-FEC) limit of 3.8 × 10−3, which shows the promising potential and feasibility of this proposal to extend multiple services from metro areas to suburban areas.

Gigabit-class optical wireless communication system at indoor distances (1.5 ÷ 4 m).

In this paper we experimentally realized bidirectional optical wireless communication (OWC) link using four channel visible LED board exploiting wavelength division multiplexing (WDM) for the downlink and infrared LED for uplink. We achieved greater than 5 Gbit/s data rate at common indoor distance (1.5 to 4 m) for downlink and 1.5 Gbit/s for uplink using commercially available LEDs. We achieved these results after a careful choice of the LED emission wavelengths and the optical filter spectra. Moreover, we investigate the optimal LED working current and the optimal modulation depth. The bit error ratios of all the channels were maintained lower than the FEC limit (3.8·10(-3)).

A Multi-Granularity Grid-Based Graph Model for Indoor Space

With the development of the Internet of Things (IoT) and indoor positioning technologies, how to manage the rapidly increasing indoor moving object data is a research topic. The fundamental issue is to consider the representation of complicated indoor space as well as the moving object. In this paper, we aim to propose a complete indoor space model that can support various indoor applications. The proposed model divides each indoor element into multigranularity grids and introduces grids as indoor primitive geometry for the representation of connectivity between indoor elements and location of moving objects. The advantage of this approach is that it can simultaneously represent the connective relationship and geometric information of indoor elements, and give more accurate description of indoor distance and direction information. Several queries of indoor applications under the shopping mall scenario are employed to illustrate the completeness and robustness of our model.

Integrated 10 Gb/s multilevel multiband passive optical network and 500 Mb/s indoor visible light communication system based on Nyquist single carrier frequency domain equalization modulation.

We propose and experimentally demonstrate a novel integrated passive optical network (PON) and indoor visible light communication (VLC) system based on Nyquist single carrier frequency domain equalization (N-SC-FDE) modulation with direct detection. In this system, a directly modulated laser and a commercially available red light emitting diode are served as the transmitters of the PON and VLC, respectively. To enable high spectral efficiency, high-speed transmission, and flexible multiple access with simplified optical network unit-side digital signal processing, multilevel, multiband quadrature amplitude modulations 128/64/16 are implemented here. VLC N-SC-FDE signals are successfully delivered a further 30 cm indoor distance after transmitting over a span of 40 km single mode fiber (SMF) together with 3 sub-band PON signals. As a proof of concept, a 10 Gb/s PON and 500 Mb/s VLC integrated system for three wired users and one wireless user is successfully achieved, which shows the promising potential and feasibility of this proposal to extend multiple services from metropolitan to suburban areas.